6. Finding the XFree86 X Server Version From a Client

The XFree86 X servers report a VendorRelease value that matches
the XFree86 version number. There have been some cases of releases where
this value wasn't set correctly. The rules for interpreting this value
as well as the known exceptions are outlined here.

For 3.3.x versions, the VendorRelease value is Mmnp.
That is, version M.m.n.p has VendorRelease set to
M * 1000 + m * 100 + n * 10 + p.
Exceptions to this are: The value wasn't incremented for the 3.3.3.1
release, and for the 3.3.4 and 3.3.5 releases the value was incorrectly
set to Mmn
(M * 100 + m * 10 + n).
This was corrected for the 3.3.6 release.

For versions 3.9.15 to 4.0.x, the VendorRelease value is
Mmnn. That is, version M.m.n has VendorRelease
set to
M * 1000 + m * 100 + n.
There have been no exceptions to this rule.

For post-4.0.2 development and release versions using the new numbering
scheme, the VendorRelease value is MMmmPPsss. That
is, version M.m.P.s has VendorRelease set to
M * 10000000 + m * 100000 + P * 1000 + s.
Note: 4.0.3 and any other 4.0.x releases will continue with the
Mmnn scheme.

The following is a code fragment taken from xdpyinfo.c that shows
how the VendorRelease information can be interpreted.